Coast FI by Age: What Your Number Looks Like at 30, 40, and 50

Your Coast FI number is not one number for life. It changes with your age, because it depends on how many years your money has left to grow. At 30, time does most of the work, so the number is small. At 50, time is shorter, so the number is much larger. This post shows what the number looks like at every age, so you can see where you stand, or where you are headed.

The assumptions used in this post

All numbers in this post use one consistent set of assumptions. Your retirement target is $1,000,000. That target comes from yearly retirement spending of $40,000 times 25, which is the same as dividing by a 4 percent withdrawal rate. You plan to retire at 65. The assumed return is 7 percent real each year. Real means after inflation. That is an assumption, not a forecast. The examples leave out taxes and fees, and they assume no new money is added after you reach Coast FI. Change any of these inputs and the numbers change too.

The 4 percent rate needs care. William Bengen published the first version in 1994. He found that a first year withdrawal of about 4.1 percent lasted for a 30 year retirement with a portfolio of 50 percent stocks and 50 percent intermediate term government bonds. The Trinity study, published in 1998, tested withdrawal rates over 30 year periods and found that 4 percent held up in most of them. Both used past data. Neither is a promise about the future.

The table: Coast FI numbers for a $1,000,000 target

Age 30, 35 years to 65: $93,700. Age 35, 30 years to 65: $131,400. Age 40, 25 years to 65: $184,200. Age 45, 20 years to 65: $258,400. Age 50, 15 years to 65: $362,400. Age 55, 10 years to 65: $508,300. Age 60, 5 years to 65: $713,000. All figures are rounded to the nearest $100. They are illustrations, not promises.

An earlier draft of this post used $95,000 at 30, $130,000 at 35, $185,000 at 40, $260,000 at 45, $360,000 at 50, $510,000 at 55, and $710,000 at 60. Each of those was close, but none followed exactly from the stated 7 percent assumption. The corrected table above does. The largest correction is at 50, where $360,000 grows to about $993,400 in 15 years at 7 percent, about $6,600 short of the target. The corrected number at 50 is $362,400.

Worked example: the same $1,000,000 target at 30, 40, and 50

Use round hypothetical numbers only. Keep the target fixed at $1,000,000, so the reader can see the effect of time alone.

At 30, step by step: 65 minus 30 equals 35 years. 1.07 to the power of 35 equals 10.68. Then $1,000,000 divided by 10.68 equals $93,663. Round that to $93,700. Check: $93,663 times 10.68 equals about $1,000,000.

At 40, step by step: 65 minus 40 equals 25 years. 1.07 to the power of 25 equals 5.43. Then $1,000,000 divided by 5.43 equals $184,249. Round that to $184,200. Check: $184,249 times 5.43 equals about $1,000,000.

At 50, step by step: 65 minus 50 equals 15 years. 1.07 to the power of 15 equals 2.76. Then $1,000,000 divided by 2.76 equals $362,446. Round that to $362,400. Check: $362,446 times 2.76 equals about $1,000,000.

Compare the three answers. At 30 you need $93,700. At 40 you need $184,200, about twice as much. At 50 you need $362,400, about twice as much again, and about four times the age 30 number. Waiting 10 years roughly doubles the amount you need today, because you lose 10 years of growth. That is the whole story of the table.

What to do at each age

At 30

At 30, a small amount saved now does a lot. Your Coast FI number is $93,700 for a $1,000,000 target. If you are not there yet, steady saving is enough. Saving $10,000 a year from $0 reaches $93,700 in about 8 years at a 7 percent real return, so you can reach Coast FI by your late 30s and still have 25 years of growth left.

At 40

At 40, your Coast FI number is $184,200. If you have saved $100,000, you are more than halfway there, since $100,000 divided by $184,200 equals about 54 percent. Saving $20,000 a year from $100,000 reaches $184,200 in about 3 years at a 7 percent real return. After 3 years you would have about $186,800. The gap closes fast when you already have a base to grow from.

At 50

At 50, your Coast FI number is $362,400. The number is larger, but it is still a number you can reach. Saving $20,000 a year from $0 reaches $362,400 in about 12 years at a 7 percent real return, which is before 65. With a base already saved, the time is shorter. The point is that the plan still works. It asks for more savings each year, not for a miracle.

Why starting late is not fatal

Starting at 50 feels late, because the number is $362,400 instead of $93,700. But the math still works in your favor in three ways. First, you still have 15 years of growth, and 15 years at 7 percent nearly triples your money. Second, you are likely earning more at 50 than at 30, so saving $20,000 a year is more realistic. Third, you can change the other inputs. Retire at 67 instead of 65 and your number falls. Spend a little less in retirement and your target falls by 25 times the saving.

Late starters also have tools that younger savers do not. Catch up contributions let workers aged 50 and over put extra money into a 401k and an IRA, above the normal limits. That extra room is made for this exact case. Check the limits for the year before you plan on them.

The mistake is to look at the age 30 number and give up. The age 30 number is not your number. Your number is the one for your age, your spending, and your retirement date. At 50, $362,400 is a large sum, but it is a sum you can reach with steady saving and time. At 60, the number is $713,000, which is large, but by then you may have a home with equity, a higher income, and fewer years of costs ahead. The plan does not expire. It just asks for more each year.

The bottom line

For a $1,000,000 target at 65 and a 7 percent real return, the Coast FI number is $93,700 at 30, $184,200 at 40, and $362,400 at 50. The same target roughly doubles each 10 years you wait. That is the cost of time. It is also the reason to start now, at whatever age you are. The number is larger at 50 than at 30, but it is still within reach with steady saving, and it still buys the same freedom: a retirement plan that growth alone can finish.

This post is for education only. It is not financial advice. Your numbers will differ based on your spending, your retirement age, your taxes, and your investments.

Sources

Investopedia, Coast FIRE: https://www.investopedia.com/terms/c/coast-fire.asp

Investopedia, The 4 percent Rule: https://www.investopedia.com/terms/f/four-percent-rule.asp

Bengen, William P., Determining Withdrawal Rates Using Historical Data, Journal of Financial Planning, October 1994: https://www.financialplanningassociation.org/article/journal/OCT94-determining-withdrawal-rates-using-historical-data

Cooley, Philip L., Hubbard, Carl M., and Walz, Daniel T., Retirement Savings: Choosing a Withdrawal Rate That Is Sustainable, Journal of Financial Planning, February 1998, the Trinity study: https://www.financialplanningassociation.org/article/journal/FEB98-retirement-savings-choosing-withdrawal-rate-sustainable

Social Security Administration, Period Life Table: https://www.ssa.gov/oact/STATS/table4c6.html

Internal Revenue Service, Retirement Plans, catch up contributions: https://www.irs.gov/retirement-plans